Several methods are currently available which can be used to study point mutations in a DNA molecule. For example, it is possible to isolate a variant cell recognized by a DNA sequence of interest, such as one thought to contain a mutation, and then sequence the cloned product, using known techniques. Alternatively, DNA to be analyzed, such as tumor DNA, can be cloned, amplified and sequenced, also using known techniques. Although it is possible, using presently-available method, to study individual DNA mutations and to determine a mutational spectrum or profile or alterations in a selected DNA sequence, to do so is time-consuming and tedious. This is due at least in part to the fact that a large number of mutants, each of which must be isolated one at a time, must be analyzed in order to get a statistically reproducible spectrum. For example, it is reasonable to assume that approximately 10 mutants per base pair (bp) of DNA sequence is necessary to give a statistically reproducible result. Thus, in the case in which the mutational spectrum of a 100 bp DNA sequence is to be determined, approximately 1000 mutants must be assessed. Using presently-available methods, each assessment requires considerable time (e.g., 1 day per mutant analyzed) and, thus, carrying out the 1000 assessments needed for a 100 bp DNA sequence is work-intensive.
In addition, presently-available methods are limited to cases in which a particular mutation is present in the germ cell of an individual or other cases in which the frequency of a particular mutation is relatively high (e.g., exceeding 0.1%). A method which would facilitate the detection of point mutations occurring at much lower frequencies, such as occur in nature, would be extremely valuable, particularly in situations such as those in which exposure to a toxic substance results in a useful diagnostic set of alterations or single base changes in genetic material.